Near L-edge Single and Multiple Photoionization of Doubly Charged Iron Ions

Abstract

Using the photon-ion merged-beams technique at a synchrotron light source, we have measured relative cross sections for single and up to five-fold photoionization of Fe 2+ ions in the energy range of 690-920eV. This range contains thresholds and resonances associated with ionization and excitation of 2p and 2s electrons. Calculations were performed to simulate the total absorption spectra. The theoretical results show very good agreement with the experimental data, if overall energy shifts of up to 2.5eV are applied to the calculated resonance positions and assumptions are made about the initial experimental population of the various levels of the Fe 2+ ([Ar]3d 6 ) ground configuration. Furthermore, we performed extensive calculations of the Auger cascades that result when an electron is removed from the 2p subshell of Fe 2+ . These computations lead to a better agreement with the measured product-charge-state distributions as compared to earlier work. We conclude that the L-shell absorption features of low-charged iron ions are useful for identifying gas-phase iron in the interstellar medium and for discriminating against the various forms of condensed-phase iron bound to composite interstellar dust grains.Unified Astronomy Thesaurus concepts: Interstellar atomic gas (833); Interstellar clouds (834); Interstellar medium (847); Interstellar absorption (831); Line intensities (2084); Atomic spectroscopy (2099); Line positions (2085); X-ray astronomy (1810); Laboratory astrophysics (2004)

Multiple photoionization for the K shell in the Fe atom

“…This can be explained by the fact that additional artificial channels are opened in the calculations of the ion yield by modifying subshell energies (Kaastra & Mewe 1993). The similar situation was obtained for the radiative and Auger cascades following the photoionization from the 1s, 2s, and 2p subshells in the Fe 2+ ion (Kučas et al 2019;Kučas et al 2020b;Schippers et al 2021). The study of the subconfigurations is more detailed than that of the configuration averages, but the highest population is pro-duced for the Fe 5+ ions in the first case.…”

“…However, the energies of the subshells were modified to account for the effective charges experienced by electrons due to presence of the vacancies (Kaastra & Mewe 1993). This often led to overestimated ion yields for the higher ionization stages (Kučas et al 2020a,b;Schippers et al 2021). In this paper we give results obtained via more consistent calculations.…”

The electronic structure and deexcitation pathways of an isolated metalloporphyrin ion resolved by metal L-edge spectroscopy

“…For resonant iron 2p inner-shell excitation of Fe 2+ ions with 3d 6 electrons, similar to cobalt ions in CoPPIX + , double ionisation is the main deexcitation process. 70 Therefore, we discuss the case z = 3, corresponding to double ionisation of CoPPIX + , here. Deexcitation of [CoPPIX 3+ ]* may lead to the formation of CoPPIX 3+ and singly to triply charged CoPPIX fragments by single or multiple losses of neutral and/or charged fragments.…”

Symbolic Evaluation of Expressions from Racah’s Algebra

“…Apart from interactive (atomic) computations, JAC also supports various representations of atomic states, including mean-field orbitals, restricted code spaces [29,30] and approximate Green function expansions [31], to name just a few. It also facilitates the computation and simulation of atomic cascades [32][33][34], by just following different excitation schemes. Figure 1 displays a brief overview about the JAC toolbox and its major features.…”